refactor(logging): replace info! macro with tracing::info! in src/model/leg/mod.rs

Aligns logging implementation to use the `tracing` crate instead of the legacy `log` crate. No functional changes introduced.

Author: joaquinbejar

src/model/leg/mod.rs

@@ -52,7 +52,7 @@
 //!
 //! // Both legs can be handled uniformly via LegAble trait
 //! use optionstratlib::model::leg::LegAble;
-//! info!("Spot delta: {}", spot_leg.delta()?);
+//! tracing::info!("Spot delta: {}", spot_leg.delta()?);
 //! # Ok(())
 //! # }
 //! ```